1. Field of Invention
The present invention relates generally to data storage, and more particularly to data storage systems that associate a retention period with stored data.
2. Discussion of Related Art
Businesses and other institutions, such as hospitals, schools, and government agencies, often use data storage systems to maintain records in electronic form. Such records may include, for example, company financial records, electronic mail (e-mail), patient medical records, student transcripts, and other types of data. It may be important to the business or institution to maintain these records in their original form for a certain period of time after their creation. That is, the business or institution may desire to prevent the records from being deleted or modified until a certain period of time has elapsed. For example, a hospital may wish to prevent modification or deletion of patient x-rays for a certain number of years after the x-rays are taken. Further, such retention of data may be mandated by law. For example, Securities and Exchange Commission (SEC) Rule 17a-4 requires that companies preserve certain financial records for a period of six years.
With conventional storage systems, users may accidentally delete or modify such records. Alternatively, malicious users may intentionally delete or modify such records, for example to conceal unscrupulous business practices or to dishonestly alter school transcripts. Whether accidental or intentional, such acts may cause an irreparable loss of data or even a violation of law. While some computer systems include a file system front end (often on a host computer rather than on a storage system) that allows files to be designated “read-only,” an administrator of the system typically has the ability to change the “read-only” status of files such that the files may be modified or deleted. Further, conventional file systems do not allow the user to specify a period of time for which data cannot be deleted or modified. That is, designating a file “read-only” means that the file cannot be deleted or modified so long as the file's read-only status is not altered.
Some storage systems store data on recording media, e.g., optical discs (such as, CD-ROM discs) which cannot be overwritten or modified. However, such systems do not allow the user to specify a retention period, as once data is written to the media it can never be deleted from the media, although the media may be physically destroyed to prevent access to the data. Such media is not reusable if it is ever desired to replace the data on the media with new data.
A technique for implementing a retention period for data stored in a storage system is disclosed in commonly assigned U.S. patent application entitled “Method and Apparatus for Data Retention in a Storage System”, filed on Dec. 9, 2003 under Ser. No. 10/731,790, which is incorporated herein by reference in its entirety and hereafter referred to as the “Data Retention Application”.